Virtuality attached node

ABSTRACT

The present invention provides a position control system for a remote-controlled vehicle, a vehicle operated by the control system, and a method for operating a remote-controlled vehicle. An electromagnetic energy receiver is configured to receive an electromagnetic beam. The electromagnetic energy receiver is further configured to determine a position of the remote-controlled vehicle relative to a position of the electromagnetic beam. The vehicle is directed to maneuver to track the position of the electromagnetic beam.

RELATED APPLICATION

This patent application is related to concurrently-filed patentapplication entitled “LASER-TETHERED VEHICLE,” bearing attorney docketnumber BOEI-1-1215, which is incorporated by reference.

FIELD OF THE INVENTION

This invention relates generally to unmanned craft and, morespecifically, to remotely controlled vehicles.

BACKGROUND OF THE INVENTION

Remote-controlled vehicles, particularly Unmanned Air Vehicles (UAVs),have been in use for years for many different applications. At a simpleend, hobbyists steer remote-controlled cars or boats or flyremote-controlled airplanes for entertainment. At a sophisticated end,military and intelligence agencies fly UAVs to conduct surveillance inhostile territories. UAVs are equipped with cameras, microphones, andother sensors to gather intelligence. These sophisticated, complex UAVsare controlled from remote stations.

Control of such devices can be a complex problem. Even high-end hobbyistUAVs have control panels that cannot be practically hand held because ofthe many levers, dials, switches, and other control devices the operatoruses to direct such a device. Moreover, transmitting the controlinformation from the many control devices, receiving and decoding theinstructions at the remote device, and executing the instructionsrepresent involved data communication problems.

In addition, a limitation particularly limiting UAVs is that, likemanned aircraft, a UAV has to have the capacity to carry enough fuel orpower to complete its mission. The longer the mission, the more fuel orpower that must be carried, and, the larger the UAV must be to carry itsown source of power. Furthermore, hovering tends to consumesubstantially more power than forward flight. Thus, UAVs commonly usefixed-wing, forward flight designs.

For example, the Pointer by AeroVironment is a fixed-wing UAV. ThePointer has a length of 6 feet with a wingspan of 9 feet. The Pointerweighs 8 pounds with a payload of 2 pounds and a battery weighing 2.2pounds. It is hand-launched by being thrown into the air. The Pointerhas a flight duration of 1.5 hours with a range of 5 miles.

However, forward-flight is not an optimal flight mode for all purposes.For example, forward-flight is not an optimal flight mode forsurveillance. A forward-flying platform moves over and may move pasttargets of interest. While a forward-flying platform can circle a targetof interest, gathering information about the target may be complicatedby moving a camera lens or other directional sensor to focus on thetarget. As a result, a hovering platform presents a more desirable pointfrom which to observe a target of interest. Forward-flight also is notoptimal for a platform to be used for relaying or redirecting signals.For these purposes it would be advantageous to have a hovering platformsuspended over a stationary ground point to redirect and relay signalsfor which a line-of-sight transmission is desirable but not possible.Such a hovering platform would enable communications or otherelectromagnetic transmission to be broadcast over buildings or otherbarriers that ordinarily would block such transmissions.

Hovering vehicles generally consume more power than forward-flyingvehicles. To try to develop a more efficient hovering vehicle, micro airvehicles (MAVs) have been created using flapping wing technologies tocreate lift. The existence of insects and small flying animals suggeststhat flapping wing technologies can be an efficient way to create lift.For one example, a collaboration between Caltech and UCLA has developedan MAV called the MicroBat. The MicroBat recently broke the world recordin flapping wing flight of an MAV with a flight lasting only 6 minutesand 17 seconds. The MicroBat carries a polymer lithium ion battery asits power source and carries a radio transceiver. The total weight ofthe MicroBat is only 12 grams. However, in flapping wing flight,aerodynamic flow properties are complex and difficult to manage. Thus,just as land-based vehicles tend not to be based on walking movements ofbipeds or quadrupeds but on simpler-to-manage rotating motivators suchas wheels, it would be simpler to effect hovering using a rotary wingdesign such as a helicopter. Unfortunately, an efficient way to sustainhovering flight for very long intervals has proven elusive.

Thus, there is an unmet need in the art for facilitating sustained,hovering flight and thereby allowing for simpler and more efficient waysto perform aerial surveillance of a target of interest or to redirectand relay electromagnetic signals from a transmission site to a receiveror other target.

SUMMARY OF THE INVENTION

The present invention provides a system and method for operating aremote-controlled vehicle and a remote-controlled vehicle operatedaccording to the system and method. A preferred embodiment of thepresent invention includes an unmanned vehicle (UAV) configured to bedirectable to a point of interest and hover over the point of interest.In contrast with known hovering vehicles that include relatively complexcontrol schemes to maintain the vehicle in a desired position,embodiments of the present invention are guided and powered by anelectromagnetic beam generated from a ground source or an aircraft.Using electromagnetic sensors on the vehicle to monitor the position ofthe electromagnetic beam, the vehicle tracks the position of theelectromagnetic beam. Thus, by controlling the position of theelectromagnetic beam, the position of the airborne vehicle can becontrolled, thereby allowing for surveillance of a desired location or asignal relay point to be positioned at a desired point in space. Otherembodiments of the present invention also convert the receivedelectromagnetic energy beam into electrical power for providing at leasta portion of the power used in operating the vehicle.

More particularly, embodiments of the present invention provide aposition control system for a remote-controlled vehicle. Anelectromagnetic energy receiver is configured to receive anelectromagnetic beam. The electromagnetic energy receiver is furtherconfigured to determine a position of the remote-controlled vehiclerelative to a position of the electromagnetic beam. The vehicle isdirected to maneuver to track the position of the electromagnetic beam.

In accordance with other aspects of the present invention, theelectromagnetic energy receiver includes at least one photoelectric cellconfigured to generate electrical power when subjected to application ofelectromagnetic energy. The photoelectric cell may include a solar cell.The electromagnetic energy receiver may be configured to receive anexternally-applied laser signal.

In accordance with still further aspects of the present invention, theelectromagnetic energy receiver includes an electromagnetic receivingarray including a plurality of electromagnetic sensors. Each of theelectromagnetic sensors is configured to generate a sensor outputindicative of an intensity of electromagnetic energy received by theelectromagnetic sensor. The vehicle is maneuvered to generally equalizethe sensor output of each of the electromagnetic sensors by maneuveringthe remote-controlled vehicle such that the electromagnetic beam isreceived toward a center of the electromagnetic receiving array. Thevehicle is further maneuvered relative to the source of theelectromagnetic beam such that the remote-controlled vehicle maintains apredetermined distance from the source of the electromagnetic beam. Thecontrol system is further configured to receive external commands foradjusting a response to the electromagnetic beam.

Additionally, in accordance with other aspects of the present invention,the remote-controlled vehicle may include an airborne vehicle, includinga rotor-lifted vehicle powered by one or more rotors or alighter-than-air vehicle, a land-based vehicle, a water-based vehicle,or a space-based vehicle.

In accordance with still further embodiments of the present invention,the vehicle may include at least one surveillance device. Thesurveillance device suitably is configured to capture data from theperspective of the remote-controlled vehicle. The surveillance devicealso suitably is configured to transmit telemetry to a telemetry stationand/or is remotely controllable from a control station. The surveillancedevice may include at least one of a camera, a microphone, a chemicalsensor, a biological sensor, a radiation detector, and an environmentalsensor. The vehicle also may include a payload delivery mechanism. Thevehicle may have a means to modulate and rebroadcast the receivedelectromagnetic power to relay information back to the source of thatpower or control station. Alternatively, the vehicle may include anelectromagnetic relay device configured to relay an electromagneticsignal from a signal source to a signal destination. The relay devicemay include an electromagnetic signal such as a communication signal oran energy weapon. The relay device may include a reflector or a relaydevice such as a microwave relay.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings.

FIG. 1 is a top view of a laser-tethered airborne device according to anembodiment of the present invention;

FIG. 2 is a side view of the device of FIG. 1;

FIG. 3 is a perspective view of the device of FIG. 1;

FIG. 4 is a perspective view of the device powered and controlled by aground station;

FIG. 5 is a laser-tethered airborne device according to anotherembodiment of the present invention;

FIG. 6 is a zone diagram of a laser receiving array of the device;

FIG. 7 is a block diagram of a laser receiving and control device usedby an embodiment of the present invention;

FIG. 8 is a yaw control device used by an embodiment of the presentinvention;

FIG. 9 is a block diagram of a control system used by an embodiment ofthe present invention;

FIG. 10 is a diagram illustrating an embodiment of the present inventionin which an airborne vehicle is tethered by an electromagnetic beam andis configured to relay an electromagnetic signal;

FIG. 11 is a side-elevational view of an alternative embodiment of thepresent invention used with a lighter-than-air vehicle;

FIG. 12 is a perspective view of the vehicle of FIG. 11 being controlledby an electromagnetic beam; and

FIG. 13 is a flowchart of a routine for using an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

By way of overview, embodiments of the present invention provide amethod for remote powering and a position control system for aremote-controlled vehicle. An electromagnetic energy receiver isconfigured to receive an electromagnetic beam. The electromagneticenergy receiver is further configured to determine a position of theremote-controlled vehicle relative to a position of the electromagneticbeam. The vehicle is directed to maneuver to track the position of theelectromagnetic beam.

FIG. 1 is a perspective view of a laser-tethered airborne device 100.The device 100 includes a structure or housing 110 which supports apropulsion system including a plurality of rotors 120. In one presentlypreferred embodiment, the rotors 120 are disposed to rotate so as togenerate thrust in a direction opposed to a gravitational force. Onepresently preferred embodiment includes a plurality of rotors 120 thatare disposed at a distance around a center of gravity of the device 100.The rotors 120 each are individually controlled by a positioning controlsystem (not shown). The speed and resultant thrust generated by each ofthe rotors 120 can be manipulated to generate a composite thrust havingcomponents directed both against the gravitational force andperpendicular to the gravitational force to control the altitude andazimuth of the device 100 relative to a position on the ground.Alternatively, the device 100 could be powered by one or more rotors120. The one or more rotors are disposed to rotate in a plane andthereby generate thrust. The provided thrust provides lift against thegravitational force and one or more rotors disposed in a perpendicularplane to provide thrust perpendicular to the gravitational force.Further alternatively, gimbaled rotors (not shown) could be used togenerate thrust to provide lift against the gravitational force andthrust perpendicular to the gravitational force.

A rotor-powered craft could include a rotor speed optimization systemsuch as that disclosed in U.S. Pat. No. 6,007,298 for an “optimum speedrotor” for improved rotorcraft performance, which is assigned to theassignee of the present invention and incorporated by reference. Use ofsuch a system would allow for optimization of rotor speed in order toprovide desired rotor output and reduce unnecessary power consumption.

An electromagnetic energy receiver 130 is disposed on the housing 110 toreceive an electromagnetic beam 140. Details of the electromagnetic beamare set forth below. The electromagnetic energy receiver 130 isconfigured to convert energy contained in the electromagnetic energybeam 140 into electrical power. The converted electrical power providesenergy to drive the rotors 120, the positioning control system (notshown), and other on-board systems on the device 100. As a result of theelectrical power being provided from a source outside the device 100,the device is operable to maintain controlled flight and support otherfunctions without an on-board power supply such as a battery, a fuelcell, or another power plant that would add size and, more pertinently,add mass and weight to the device 100. As previously described, addingmass to the device 100 is highly undesirable because additional massdictates additional thrust requirements which, in turn, result inadditional equipment mass to generate the additional thrust. In otherwords, beaming power to the device 100 allows the device 100 to beadvantageously small and lightweight to reduce the cross-sectionaltarget presentation, complexity, and cost of the device 100.

The electromagnetic energy receiver 130 and the positioning controlreceiver are further configured to respond to a projected position ofthe electromagnetic beam 140. As will be further described below, in onepresently preferred embodiment the electromagnetic energy receiver 130includes a plurality of photocells, such as solar cells, to receive theelectromagnetic beam 140 and generate electrical power. In one presentlypreferred embodiment, the electromagnetic beam receiver 130 includesGaSb and Ge cells. These cells are available with quantum efficienciesas high as around 95%. Other photocells, including InGaAsP or InPphotocells also provide suitable power conversion in desirable operatingranges that are described further below.

An electromagnetic beam 140 at a wavelength of 1.064 μm provides aworkable solution, as will be further described below. At thiswavelength, a number of solar cell types can be used to collect energyfor the device. Of these, two types currently are readily availablesolar cells widely used in the infrared range. A Ge solar cell is oftenused as the bottom cell in high efficiency multi-junction solar cells,mainly for space applications. A GaSb solar cell is commonly used inthermo-photovoltaic applications. Although the Ge and GaSb cells arewidely available, their energy conversion efficiencies are notparticularly high because both have bandgaps that are slightly lowerthan an optimal level. In general, to get good conversion efficienciesthe semiconductor band gap would have to be smaller but close in energyto that of the incident radiation. For example, a bandgap smaller than1.064 eV is desirable for an energy source having a wavelength of 1.064μm. Ge cells have an efficiency of approximately 16% whereas GaSbactually have a slightly higher efficiency of approximately 20% eventhough Ge cells have a more favorable bandgap. Better conversionefficiencies would be possible at the 1.064 μm wavelength with the solarcells made of a semiconductor with a bandgap closer to 1.05 eV. Suchcells are not commercially available but could be created using amaterial of composition In_(0.85)Ga_(0.15)As_(0.4)P_(0.6) grown on anInP substrate. Such a cell could provide a total conversion efficiencyof up to 43% with a fill factor of 83%.

Also, the use of a plurality of photocells allows the positioningcontrol system (not shown) coupled with the electromagnetic energyreceiver 130 to respond to a projected position of the electromagneticbeam 140. More specifically, each of the photocells included in theelectromagnetic energy receiver 130 are operable to generate electricalpower in proportion to a specific intensity of the electromagnetic beam140 striking each of the photocells. Accordingly, the positioningcontrol system (not shown) can be programmed to control the propulsionsystem to balance the power output of the photocells in theelectromagnetic energy receiver 130 by a suitable adjustment of thevehicle position.

For example, the positioning control system (not shown) suitablycontrols the propulsion system to maintain a position of the device 100.The positioning control system (not shown) suitably is programmed tobalance a vertical and horizontal attitude such that the power output ofthe photocells is approximately equal. Similarly, the positioningcontrol system (not shown) suitably is programmed to maintain acomposite energy output of the photocells in the electromagnetic energyreceiver 130. As a result, the positioning control system (not shown)can maintain the device 100 at a distance and an attitude relative tothe received electromagnetic beam 140 such that the electromagnetic beam140 serves as a virtual tether for the device 100.

According to one exemplary embodiment, the device 100 is equipped withat least one array 150 of photocells, such as solar cells, disposed toreceive ambient electromagnetic energy and convert it to auxiliaryelectrical power to power on-board systems of the device 100. Thephotocell arrays 150 suitably include Si solar cells coupled withcapacitors to provide a backup power source. The auxiliary electricalpower provided by the photocell arrays 150 suitably is used to provideadditional or backup power for the device. For example, if the device100 loses contact with the electromagnetic beam 140 for any reason, thepositioning control system (not shown) can use the auxiliary electricalpower to bring the device to a soft, controlled landing. In onepresently preferred embodiment, the positioning control system (notshown) will slowly lower the device 100 to earth and/or drive the device100 toward the source of the electromagnetic beam 140 to reestablish thepower link between the device 100 to its base.

One presently preferred embodiment of the device is a substantiallydisk-shaped object about 12-14 inches in diameter with theelectromagnetic energy receiver 130 on one side. The size of the vehicleis chosen so as to minimize the power utilized for remote poweredflight. One presently preferred embodiment includes fourelectrically-powered brushless DC motors to drive the rotors 120. Afour-rotor design is used because it simplifies the control system forthe device. By varying the torque applied to the four rotors 120, roll,pitch, yaw, and overall thrust can be controlled. This strategy forcontrol is feasible for a small size craft because the rotor inertia isvery low and the control bandwidth is very high. If desired, additionaldamping suitably is provided by gyroscopic feedback.

FIG. 2 shows the device 100 receiving the electromagnetic beam 140 froma control station 200. In one exemplary embodiment, the control station200 suitably is a ground-based vehicle, although the control station 200could be a fixed, ground-based control station, an aerial controlstation such as a helicopter or other flying platform or a navalvehicle. The control station 200 includes a beam generator 210 forgenerating the electromagnetic beam 140. As previously described, theelectromagnetic beam 140 suitably serves as a tether for the device.Thus, by steering the beam generator 210, operators of the controlstation 200 can position the device 100 in altitude and azimuth. As thepositioning control system (not shown) of the device will strive toequalize the electrical power output of the photocells in theelectromagnetic energy receiver 130 (FIG. 1), the device 100 will moveto follow the projection of the electromagnetic energy beam. In onepresently preferred embodiment, the beam generator 210 is a lasergenerator. The power output of the laser generator suitably is balancedto provide sufficient power for the device 100 (FIG. 1) withoutgenerating a destructive degree of power. Similarly, the wavelength andpower of the laser generator are selected to avoid eye injuries fromscattering of the electromagnetic beam 140 while, at the same time,providing a wavelength with efficient atmospheric penetration. Selectionof the wavelength also should be made with respect to the photocellsused in the electromagnetic energy receiver 130 so that theelectromagnetic beam 140 will provide energy at a wavelength that can beefficiently converted by the photocells. Similarly, the photocellssuitably are chosen for efficiency at a laser wavelength having goodatmospheric penetration while reducing potential eye injury.

In one presently preferred embodiment, the laser generator is operableto generate a 1.064 μm-wavelength Nd:YAG laser. Othercommercially-available compact, single mode high power lasers in the100-300W range are available in the 1.07 μm range, along with solarcells that operate at a high efficiency at this wavelength range. Alaser at this frequency emits sufficient energy to provide a convertibleenergy source for the device 100. A laser operating at this wavelengthhas a transmission coefficient of about 70% at 1 km. Beam quality isalso a consideration because, in one presently preferred embodiment, theelectromagnetic beam not only serves as a power source but also ascommunications conduit and vehicle control system. A 1.064 μm wavelengthrepresents a compromise between concerns of power output, conversionefficiency, atmospheric transmission, eye-safety, and beam quality.

A suitable atmospheric window exists at the 1.06-1.07 μm wavelengthbecause the laser beam can penetrate earth's atmosphere with minimumattenuation. In one presently preferred embodiment, an estimated powerbudget for the device 100 is in the range of 8-10 watts. Therefore, thedevice can collect sufficient power from a 50-100W watt laser at adistance of 1 to 2 km.

In one presently preferred embodiment, the beam generated by the beamgenerator 210 is expanded to minimize spread perpendicular to an axis ofprojection of the beam over a proposed range of operation. Minimizingspread is desirable to prevent wasted scattering of the energy projectedby the beam generator 210 so as not to waste power as well as to allowthe positioning control system (not shown) to be able to project aconstant amount of power along the length of its virtual tether and alsomeasure the length of the tether. An electromagnetic beam of roughly10-15 cm in diameter is considered suitable. Using a 50W laser, when thebeam is expanded over a 10 cm circle, the incident power is 0.6 W/cm². A10 cm diameter beam does not have substantially any beam divergence fora distance of 1-2 kilometers.

The electromagnetic energy beam 130 generated by the beam generator 210also can be modulated to communicate additional control information tothe device 100. If the positioning control system (not shown) issuitably equipped, modulated signals included in the electromagneticbeam 130 can be used to adjust how the device 100 responds to theelectromagnetic energy beam 130. For example, this response can controlsurveillance devices (not shown) and telemetry, as well as otherfunctions of the device. It will be appreciated that such control alsocould be transmitted using a separate modulated electromagnetic energybeam or RF signals.

Referring now to FIGS. 3 and 4, the housing 110 has generally curvedsides 310 around most of the perimeter of the device 100. The curvedsides 310 present a smaller drag profile to prevailing cross winds thando generally flat sides. However, in one presently preferred embodimentof the device 100, the housing includes at least one flat end 320 onwhich the electromagnetic energy receiver 130 is disposed. Disposing theelectromagnetic energy receiver 130 on a flat surface simplifies thebalancing of the energy received by the electromagnetic energy receiver130. FIG. 3 also shows an edge of a photocell array 150. The photocellarrays 150 generally are positioned on an upper surface of the housing110 of the device to capture sunlight which generally will reach theupper surface of the housing 110. The photocell arrays 150 are disposedon the housing 110 around and between the rotors 120. With thisarrangement, the photocell arrays 150 make use of otherwise unused,available surface area on the housing 110 without obstructing operationof the rotors 120.

FIG. 5 is another embodiment of the device 500. The device 500 includesa housing 510 that features rounded sides 520 around an entire perimeterof the housing 510, a plurality of rotors 120, and an electromagneticenergy receiver 530 mounted on a face of the housing 510 instead of on aside of the housing 510 as used in the first embodiment of the device100 (FIGS. 1-4). When the device 500 is powered by an electromagneticbeam 540 projected from substantially below the device 500, theelectromagnetic energy receiver 530 advantageously may be disposed on anlower face of the device 500. Similarly, when the device 500 is poweredby an electromagnetic beam 540 projected from substantially above thedevice 500, the electromagnetic beam receiver 530 advantageously may bedisposed on an upper face of the device 500. In either case, when theelectromagnetic energy receiver 530 is disposed on a face of the device500, the housing 510 of the device 500 advantageously can employ roundedsides 520 around an entire perimeter of the device 500 with aerodynamicbenefits such as, for example, reduced drag to crosswinds on all sides.

FIG. 6 is a zone diagram of an electromagnetic energy receiver array600. As previously described, energy received by the array 600 is usedboth to generate power for the device and to measure the position of thedevice. As previously discussed, the device can be programmed to tetheritself to a projected position of the electromagnetic energy beam (notshown in FIG. 6) to remain aligned with the beam. It will be appreciatedthat “the device” suitably refers to the device 100 (FIGS. 1-4) and thedevice 500 (FIG. 5). To support such alignment, the array 600 suitablyis divided into a plurality of angular zones 610 and radial zones 620.These zones provide carrier collection electrodes (grid) for efficientphotoelectric power conversion. Both the angular zones 610 and radialzones 620 are also suitably are used to determine if the beam is movingrelative to the array 600 either as the result of the movement of thebeam or movement of the device. It will be appreciated that if the arrayincluded only angular zones 610, as position of the array 600 relativeto the beam changed along a single angular direction, the array 600would not indicate the relative movement until the beam moved off thearray 600. Similarly, if the array included only radial zones 620, asposition of the array 600 relative to the beam changed within a singleradial zone 620, the array 600 would not indicate the relative movementuntil the beam moved off the array 600. Thus, using an array 600 dividedinto zones 610 and 620 provides outputs indicating relative movementbetween the beam and the array 600 so that the device can align itselfto the electromagnetic energy beam.

In one exemplary embodiment, the electromagnetic energy receiversuitably is formatted into four quadrants, 650, 660, 670, and 680.Employing quadrants 650-680 is useful for controlling operation of thedevice 100, as will be further explained below.

FIG. 7 is a block diagram of a control system 700 used by the device 100(FIG. 1) and the device 500 (FIG. 5), hereinafter referred to as “thedevice.” To minimize power consumption and mass, while also providingoptimal miniaturization, a control system using low-powerapplication-specific integrated circuits is desirable, although thecontrol system 700 can include off-the shelf components. The controlsystem 700 is configured to generate flight control signals thatmaintain the device in alignment with the electromagnetic beam. Althougha variety of control systems are useable with the device, one presentlypreferred embodiment of the present invention uses an analog servo loopcontrol system with proportional-integration-differentiation (PID). Theloop couples the electromagnetic energy receiver 710 with the motors 720powering the rotors 120 (FIGS. 1-4). Center locking of the solar cellassembly to the laser beam is achieved when the difference of twocross-quadrant outputs 730 and 740 of the photocell array, for examplethe difference between quadrant 650 and quadrant 680 and quadrant 660and quadrant 670 (FIG. 6) in each servo loop approaches zero. When thepower of all quadrants is equal, the energy received from thefour-quadrant solar cell reaches its maximum level, thereby signifyingthe device is centered on the electromagnetic beam tether. Accordingly,the control system 700 controls the pitch of the device relative to theground and the roll of the device around an axis perpendicular to theplane of the electromagnetic energy receiver.

FIG. 8 is a yaw control device 800 used by the device 100 (FIGS. 1-4)and 500 (FIG. 5). Along with the control system 700 (FIG. 7) thatadjusts the pitch and roll of the device around an axis generallydefined by the electromagnetic energy beam 810, the yaw control devicemaintains the yaw of the device to keep the electromagnetic energyreceiver facing the electromagnetic energy beam. In one presentlypreferred embodiment, the yaw control device 800 includes an aperture820 at a center of the electromagnetic energy receiver 830. Behind theaperture 820 is a channel 840 leading toward a center of the device. Ata distal end of the channel 840 opposite the aperture 820 is a segmentedphotodiode 850. When the yaw of the device is properly aligned so thatthe device faces the electromagnetic energy beam 810, energy from theelectromagnetic energy beam 810 falls equally on both detector halves860. Any change in the yaw of the device will increase energy receivedby one detector half 860 at the expense of energy received by the otherdetector half 860. The rotors 120 (FIG. 1) can be powered to realign thedevice to face into the electromagnetic energy beam 810. On the otherhand, a lateral translation of the device can be distinguished from ayaw rotation because a lateral translation will change the energyreceived by both detector halves 860 equally, thus involving no yawadjustment.

FIG. 9 is a block diagram of a control system 900 used by an embodimentof the present invention. The control system 900 directs flight of thedevice 100 (FIGS. 1-4) and 500 (FIG. 5) and other supported functionssuch as control of surveillance devices and telemetry. The controlsystem 900 includes a processor 902 which centrally directs flight andother operations according to preprogrammed instructions and receivedcommands. The processor 902 interacts with the motion control system 904which controls operation of rotor motors 906 as previously described inconnection FIG. 7. The processor 902 also interfaces with a verticalreference sensor 908, inclination sensors 910 and 912, and a yaw sensor914 (FIG. 8) to control. Using the sensors 908-914, the processor 902can interact with the motion control system 904 to maintain the devicein level flight at an appropriate altitude and orientation.

For controlling flight operations, the processor 902 also interacts witha power management controller 916 that monitors power received by thearray 922 of photo cells acting as the electromagnetic beam receiver 130(FIG. 1) receiving the electromagnetic beam 924 and the solar cells 918(FIGS. 1, 3, and 4) configured to receive ambient radiation. The powermanagement controller 916 provides input to the processor 902 regardingavailable power for flight operations. The processor 902 also interactswith a position sensing module 920 which receives position data from thereceiver photocells 922 regarding the position of the electromagneticbeam 924 as previously described in connection with FIGS. 6, 7, and 9.

For responding to commands and controlling other supported functions,the processor also interacts with an RF transceiver 928 and surveillancedevices such as a microphone 930, and a camera 932 operating inside oroutside the spectrum of visible light. It will be appreciated that otherdetection devices, for non-limiting examples including of a chemicalsensor, a biological sensor, a radiation detector, and an environmentalsensor. Instead of a sensor, the processor 902 also suitably may directa payload delivery system for transporting a payload object having asize and mass within operational capabilities of the remote-controlledvehicle.

In one presently preferred embodiment the transceiver is used as alocation beacon which can aid the recovery of the device 100 in theevent that the device link with its power source has been permanentlysevered. The power to this beacon transceiver will be provided by thesolar cells on the top surface of the device and or any backup powerreserves. The RF transceiver 928 suitably includes a multiple-bandtransceiver configured receive input and transmit output at the sametime. The RF transceiver 928 is configured to transmit telemetry tocontrol stations. The RF transceiver 928 also suitably is configured totransmit data captured by the microphone 930 and the camera 932. The RFtransceiver 928 also is configured to receive commands from controlstations to control onboard flight and support operations. For example,RF commands can be transmitted to the RF transceiver to direct thedevice to land, to enable or disable the microphone 930 and camera, orto indicate other directives. In one presently preferred embodiment, alow-power RF transceiver in the 902-928 MHz or 2.4 GHz frequency rangeis desirable, similar to the frequency range used in cordlesstelephones. In addition to or instead of the RF transceiver 928, thedevice also can receive commands through modulated laser signals 940received via an optical interface 942. The optical interface 942 iscoupled with the processor 902 allowing the processor to respond todirectives received via the optical interface 940.

FIG. 10 is a diagram illustrating the device 100 tethered by anelectromagnetic beam 140 and configured to relay an electromagneticsignal 1000. The device 100 is flown to a relay point where the devicecan relay an electromagnetic signal 1000 from a signal source 1010 to asignal destination 1010. The device 100, as previously described inconnection with FIG. 2, receives power and direction from anelectromagnetic beam 140 generated by a beam generator 210 associatedwith a control station 200. In this case, the control station 200 is amobile vehicle capable of carrying and powering the beam generator 210.By directing the electromagnetic beam 140 and/or transmitting RF signalsto the device, operators of the control station 200 can control theposition of the device 100.

The signal source 1010 is not in a line-of-sight with the signaldestination 1020. However, using the device 100, the signal 1000 can beredirected or relayed from the signal source 1010 to the signaldestination 1020. The electromagnetic beam 140 can be directed to placethe device 100 to a point from which it can redirect or relay thesignal. To enable the device 100 to relay the signal 1000, a reflector1030, such as a mirror, is mounted on an underside of the device 100. Inaddition to moving the device 100, the reflector 1030 suitably ismounted on a movable mount (not shown) adjustable by signals from thecontrol station 200 via the electromagnetic beam 140 or RF signals.

The electromagnetic signal 1000 suitably is an electromagneticcommunications signal, such as a modulated laser signal, generated by acommunications transmitter (not shown) and to be received by acommunications receiver (not shown). The relay device, instead of areflector, could be a microwave relay or other communications relaysuitable for relaying such a signal. Alternatively, the electromagneticsignal 1000 could be an electromagnetic weapon beam such as ahigh-powered laser. The electromagnetic weapon beam suitably isgenerated by a beam weapon (not shown) and directed toward a target (notshown).

FIG. 11 is a side-elevational view of an alternative embodiment of thepresent invention used with a lighter-than-air vehicle 1100. The device1100 suitably includes a chamber 1102 such as a balloon, dirigible,blimp or other lighter-than-air device. Methods for generating lift withsuch devices is accomplished with gases having a lesser density than anambient atmosphere, by heating ambient air, or by other methods known inthe art. Coupled to the chamber are a number of fins 1104 which suitablyinclude control surfaces for steering the device 1100 in pitch or yaw.Also coupled with the chamber 1102 is a control housing 1106. Thecontrol housing 1106 includes control devices suitable to receive andprocess the electromagnetic beam (not shown in FIG. 11) for controllingoperation of the device 1100. The housing 1106 supports one or morethrust devices 1108. The thrust devices 1108 can be gimbaled to providelift and/or thrust. The chamber 1102 provides lift as previouslydescribed, thus, the thrust devices 1108 are configured to providesupplemental lift to assist in holding payload aloft and/or forcontrolling vertical positioning of the device 1100. In addition, asteering thrust device 1110 may be included in the device 1100 toprovide another control mechanism. Coupled to the device 1100 is anelectromagnetic beam receiver 1120. The electromagnetic beam receiver1120, as previously described, receives the electromagnetic beam forpurposes of at least one of directing a position of the device 1100 andreceiving power for operating systems onboard the device 1100.

FIG. 12 is a perspective view of the device 1100 of FIG. 11 beingcontrolled by an electromagnetic beam 140. The electromagnetic beam 140is directed to a location where the device 1100 is desired. Aspreviously described, as the electromagnetic beam 140 is moved, theelectromagnetic beam receiver 1120 generates a control signalrepresentative of the position of the electromagnetic beam receiver 1120is positioned relative to the electromagnetic beam 140. Responding tothe control signal, a positioning system, housed in the housing 1106,directs the thrust device 1108 and, if included, the steering device1110 and control surfaces associated with the fins 1104, to direct thedevice 1100 to track the location of the electromagnetic beam 140. Bymeasuring signal strength or other means, the position of the device1100 relative to the source (not shown) of the electromagnetic beam 140can be controlled. By modulating and decoding pulses embedded in theelectromagnetic signal 140, by transmitting RF commands, or other means,commands can be given to the device 1100 to further direct itsoperations.

FIG. 13 is a flowchart of a routine 1300 for using an embodiment of thepresent invention. The routine 1300 begins at a block 1302 with thelaunch of the device. At a block 1304, the device receives energy froman electromagnetic energy beam and converts it into electrical power tocreate lift to fly the device. Once in flight, at a decision block 1306it is determined if the pitch and roll of the device are correct asdescribed in connection with FIG. 7. If the pitch and roll are notcorrect, at a block 1308 the pitch and roll are adjusted. On the otherhand, if the pitch and roll are correct, at a decision block 1310 it isdetermined if the yaw of the device is correct as described inconnection with FIG. 8. If the yaw is not correct, at a block 1312 theyaw is adjusted. On the other hand, if the yaw is correct, at a decisionblock 1314 it is determined if the distance from the source is correct.In one presently preferred embodiment, the distance can be determined bya conventional ranging function by beaming a signal from a controlstation to the airborne device or vice versa and measuring the delay ofthe return signal. If the distance is not correct, at a block 1316 thedistance is adjusted.

It will be appreciated that the principles used for controlling and/orproviding power to the remote-controlled vehicle are equally applicableto other than airborne vehicles. To name a few non-limiting examples,the methods for controlling and powering a remote-controlled vehicle areworkable with rolling or hovering land-based vehicles, space-basedvehicles configured to operate in a partial vacuum, and submersible,floating, or hovering water-based vehicles as well.

If at the decision block 1314 the distance is determined to be correct,at a decision block 1318 it is determined if programming changes arebeing received. Such programming changes suitably include changes indistance from the control station. If it is determined at the decisionblock 1318 that programming changes are being received, the programmingchanges are implemented at a block 1320 where operations of the airbornedevice are adjusted.

On the other hand, if it is determined at the decision block 1318 thatno programming changes are being received, at a block 1322 the deviceexecutes whatever support functions for which the device may be used.The device may be used for surveillance, relaying an electromagneticsignal, delivery of a payload, or another function.

At a decision block 1324 it is determined whether flight is to becontinued. Flight might be terminated either by a landing signal beingreceived or the airborne device losing its power source supplied by theexternal electromagnetic beam. If it is determined at the block 1324that flight is to be continued, the routine 1300 continues at the block1304 with the receipt and conversion of the energy beam. On the otherhand, if it is determined at the block 1324 that the flight is beingterminated, the routine 1300 ends at a block 1326 with the landing ofthe airborne device. It will be appreciated that all of these steps ofthe routine 1300 can be performed simultaneously or in a different orderthan shown in FIG. 13.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

1. A control system for a remote-controlled vehicle, the control system comprising: an electromagnetic energy receiver configured to receive an electromagnetic beam, the electromagnetic energy receiver including: an electromagnetic energy converter configured to convert energy received from the electromagnetic beam and generate electrical power; and a beam position sensor configured to generate a control signal indicative of a position of the electromagnetic energy receiver relative to a position of the electromagnetic beam and generate a control; and a propulsion control system configured to receive at least some of the electrical power and the control signal and further configured to generate propulsion commands to direct the vehicle to the position of the electromagnetic beam.
 2. The system of claim 1, wherein the electromagnetic energy receiver includes at least one photoelectric cell configured to generate electrical power when subjected to application of electromagnetic energy.
 3. The system of claim 2, wherein the photoelectric cell includes a solar cell.
 4. The system of claim 1, wherein the electromagnetic energy receiver is configured to receive an externally-applied laser signal.
 5. The system of claim 1, wherein the electromagnetic energy receiver includes an electromagnetic receiving array including a plurality of electromagnetic sensors, each of the electromagnetic sensors being configured to generate a sensor output indicative of an intensity of electromagnetic energy received by the electromagnetic sensor.
 6. The system of claim 5, wherein the propulsion control system is further configured to receive the sensor output of each of the electromagnetic sensors.
 7. The system of claim 6, wherein the propulsion control system is further configured to generate propulsion commands directed to maneuvering the vehicle to generally equalize the sensor output of each of the electromagnetic sensors by maneuvering the remote-controlled vehicle such that the electromagnetic beam is received toward a center of the electromagnetic receiving array.
 8. The system of claim 7, wherein the propulsion control system is further configured to generate propulsion commands directed to maneuvering the remote-controlled vehicle relative to the source of the electromagnetic beam such that the remote-controlled vehicle maintains a predetermined distance from the source of the electromagnetic beam.
 9. The system of claim 8, wherein the propulsion control system is further configured to receive external commands for adjusting a response to the electromagnetic beam.
 10. The system of claim 1, wherein the remote-controlled vehicle includes an airborne vehicle.
 11. The system of claim 10, wherein the propulsion control system is further configured to maintain the airborne vehicle at a level attitude.
 12. The system of claim 10, further comprising a propulsion system including at least one rotor disposed to generate lift.
 13. The system of claim 12, wherein the propulsion control system is further configured to optimize a speed of the at least one rotor to optimize power consumption of the at least one rotor.
 14. The system of claim 12, wherein the propulsion system includes a plurality of individually controllable lift rotors, each of the individually controllable lift rotors being further configured to generate a variable quantity of thrust such that a composite thrust of the plurality of individually controllable lift rotors provides at least one of a lift and a thrust component in a direction generally perpendicular to the lift.
 15. The system of claim 10, wherein the propulsion system includes at least one rotor disposed to generate thrust in a direction generally perpendicular to the lift.
 16. The system of claim 10, wherein the airborne vehicle includes a hovering vehicle configured to generate sufficient lift to support the airborne vehicle aloft.
 17. The system of claim 10, wherein the airborne vehicle includes a lighter-than-air vehicle.
 18. The system of claim 1, wherein the remote-controlled vehicle includes a land-based vehicle.
 19. The system of claim 1, wherein the remote-controlled vehicle includes a water-based vehicle configured to operate at least one of on the surface or under the surface of a body of water.
 20. The system of claim 1, wherein the remote-controlled vehicle includes a space-based vehicle configured to operate in at least a partial vacuum.
 21. The system of claim 1, further comprising a plurality of auxiliary solar cells disposable on a surface of the remote-controlled vehicle, the plurality of auxiliary solar cells being configured to generate auxiliary electrical power from ambient light.
 22. The system of claim 21, wherein the propulsion control system is further configured to generate propulsion commands to bring the remote-controlled vehicle to a controlled stop when contact with the electromagnetic beam is lost.
 23. A remote-controlled vehicle comprising: a vehicle housing; an electromagnetic energy receiver coupled with the housing and configured to receive an electromagnetic beam, the electromagnetic energy receiver including: an electromagnetic energy converter configured to convert energy received from the electromagnetic beam and generate electrical power; and a beam position sensor configured to generate a control signal indicative of a position of the electromagnetic energy receiver relative to a position of the electromagnetic beam and generate a control; a propulsion control system configured to receive at least some of the electrical power and the control signal and further configured to generate propulsion commands to direct the vehicle to the position of the electromagnetic beam; and a propulsion system disposed in the housing, the propulsion system being further configured to receive the propulsion commands.
 24. The vehicle of claim 23, wherein the electromagnetic energy receiver includes at least one photoelectric cell configured to generate electrical power when subjected to application of electromagnetic energy.
 25. The vehicle of claim 24, wherein the photoelectric cell includes a solar cell.
 26. The vehicle of claim 23, wherein the electromagnetic energy receiver is configured to receive an externally-applied laser signal.
 27. The vehicle of claim 23, wherein the electromagnetic energy receiver includes an electromagnetic receiving array including a plurality of electromagnetic sensors, each of the electromagnetic sensors being configured to generate a sensor output indicative of an intensity of electromagnetic energy received by the electromagnetic sensor.
 28. The vehicle of claim 27, wherein the propulsion control system is further configured to receive the sensor output of each of the electromagnetic sensors.
 29. The vehicle of claim 28, wherein the propulsion control system is further configured to generate propulsion commands directed to maneuvering the vehicle to generally equalize the sensor output of each of the electromagnetic sensors by maneuvering the remote-controlled vehicle such that the electromagnetic beam is received toward a center of the electromagnetic receiving array.
 30. The vehicle of claim 29, wherein the propulsion control system is further configured to generate propulsion commands directed to maneuvering the remote-controlled vehicle relative to the source of the electromagnetic beam such that the remote-controlled vehicle maintains a predetermined distance from the source of the electromagnetic beam.
 31. The vehicle of claim 30, wherein the propulsion control system is further configured to receive external commands for adjusting a response to the electromagnetic beam.
 32. The vehicle of claim 23, wherein the remote-controlled vehicle includes an airborne vehicle.
 33. The vehicle of claim 32, wherein the propulsion control system is further configured to maintain the airborne vehicle at a level attitude.
 34. The vehicle of claim 32, further comprising a propulsion system including at least one rotor disposed to generate lift.
 35. The vehicle of claim 34, wherein the propulsion control system is further configured to optimize a speed of the at least one rotor to optimize power consumption of the at least one rotor.
 36. The vehicle of claim 34, wherein the propulsion system includes a plurality of individually controllable lift rotors, each of the individually controllable lift rotors being further configured to generate a variable quantity of thrust such that a composite thrust of the plurality of individually controllable lift rotors provides at least one of a lift and a thrust component in a direction generally perpendicular to the lift.
 37. The vehicle of claim 32, wherein the propulsion system includes at least one rotor disposed to generate thrust in a direction generally perpendicular to the lift.
 38. The vehicle of claim 32, wherein the airborne vehicle includes a hovering vehicle configured to generate sufficient lift to support the airborne vehicle aloft.
 39. The vehicle of claim 32, wherein the airborne vehicle includes a lighter-than-air vehicle.
 40. The vehicle of claim 23, wherein the remote-controlled vehicle includes a land-based vehicle.
 41. The vehicle of claim 23, wherein the remote-controlled vehicle includes a water-based vehicle configured to operate at least one of on the surface or under the surface of a body of water.
 42. The vehicle of claim 23, wherein the remote-controlled vehicle includes a space-based vehicle configured to operate in at least a partial vacuum.
 43. The vehicle of claim 23, further comprising a plurality of auxiliary solar cells disposable on a surface of the remote-controlled vehicle, the plurality of auxiliary solar cells being configured to generate auxiliary electrical power from ambient light.
 44. The vehicle of claim 43, wherein the propulsion control system is further configured to generate propulsion commands to bring the remote-controlled vehicle to a controlled stop when contact with the electromagnetic beam is lost.
 45. A remote-controlled vehicle operation system comprising: a remote-controlled vehicle including: a vehicle housing; an electromagnetic energy receiver coupled with the housing and configured to receive an electromagnetic beam, the electromagnetic energy receiver including: an electromagnetic energy converter configured to convert energy received from the electromagnetic beam and generate electrical power; and a beam position sensor configured to generate a control signal indicative of a position of the electromagnetic energy receiver relative to a position of the electromagnetic beam and generate a control; a propulsion control system configured to receive at least some of the electrical power and the control signal and further configured to generate propulsion commands to direct the vehicle to the position of the electromagnetic beam; and a propulsion system disposed in the housing, the propulsion system further configured to receive the propulsion commands; and an electromagnetic beam generator configured to generate the electromagnetic beam.
 46. The system of claim 45, wherein the electromagnetic energy receiver includes at least one photoelectric cell configured to generate electrical power when subjected to application of electromagnetic energy.
 47. The system of claim 46, wherein the photoelectric cell includes a solar cell.
 48. The system of claim 45, wherein the electromagnetic energy receiver is configured to receive an externally-applied laser signal.
 49. The system of claim 45, wherein the electromagnetic energy receiver includes an electromagnetic receiving array including a plurality of electromagnetic sensors, each of the electromagnetic sensors being configured to generate a sensor output indicative of an intensity of electromagnetic energy received by the electromagnetic sensor.
 50. The system of claim 49, wherein the propulsion control system is further configured to receive the sensor output of each of the electromagnetic sensors.
 51. The system of claim 50, wherein the propulsion control system is further configured to generate propulsion commands directed to maneuvering the vehicle to generally equalize the sensor output of each of the electromagnetic sensors by maneuvering the remote-controlled vehicle such that the electromagnetic beam is received toward a center of the electromagnetic receiving array.
 52. The system of claim 51, wherein the propulsion control system is further configured to generate propulsion commands directed to maneuvering the remote-controlled vehicle relative to the source of the electromagnetic beam such that the remote-controlled vehicle maintains a predetermined distance from the source of the electromagnetic beam.
 53. The system of claim 52, wherein the propulsion control system is further configured to receive external commands for adjusting a response to the electromagnetic beam.
 54. The system of claim 45, wherein the remote-controlled vehicle includes an airborne vehicle.
 55. The system of claim 54, wherein the propulsion control system is further configured to maintain the airborne vehicle at a level attitude.
 56. The system of claim 54, further comprising a propulsion system including at least one rotor disposed to generate lift.
 57. The system of claim 56, wherein the propulsion control system is further configured to optimize a speed of the at least one rotor to optimize power consumption of the at least one rotor.
 58. The system of claim 56, wherein the propulsion system includes a plurality of individually controllable lift rotors, each of the individually controllable lift rotors being further configured to generate a variable quantity of thrust such that a composite thrust of the plurality of individually controllable lift rotors provides at least one of a lift and a thrust component in a direction generally perpendicular to the lift.
 59. The system of claim 54, wherein the propulsion system includes at least one rotor disposed to generate thrust in a direction generally perpendicular to the lift.
 60. The system of claim 54, wherein the airborne vehicle includes a hovering vehicle configured to generate sufficient lift to support the airborne vehicle aloft.
 61. The system of claim 54, wherein the airborne vehicle includes a lighter-than-air vehicle.
 62. The system of claim 45, wherein the remote-controlled vehicle includes a land-based vehicle.
 63. The system of claim 45, wherein the remote-controlled vehicle includes a water-based vehicle configured to operate at least one of on the surface or under the surface of a body of water.
 64. The system of claim 45, wherein the remote-controlled vehicle includes a space-based vehicle configured to operate in at least a partial vacuum.
 65. The system of claim 45, further comprising a plurality of auxiliary solar cells disposable on a surface of the remote-controlled vehicle, the plurality of auxiliary solar cells being configured to generate auxiliary electrical power from ambient light.
 66. The system of claim 65, wherein the propulsion control system is further configured to generate propulsion commands to bring the remote-controlled vehicle to a controlled stop when contact with the electromagnetic beam is lost.
 67. The system of claim 45, wherein the electromagnetic beam generator is a laser generator.
 68. The system of claim 67, wherein the laser generator generates a laser beam having a wavelength of approximately 1.064 μm.
 69. A method for operating a remote-controlled vehicle, the method comprising: receiving an electromagnetic beam; converting the electromagnetic beam into electrical power to provide at least a portion of the power used by the remote-controlled vehicle; determining a position to which the electromagnetic beam is directed; and maneuvering the remote-controlled vehicle to align a position of the remote-controlled vehicle with the position to which the electromagnetic beam is directed.
 70. The method of claim 69, wherein the electromagnetic beam is received using at least one photoelectric cell configured to generate electrical power when subjected to application of electromagnetic energy.
 71. The method of claim 70, wherein the photoelectric cell includes a solar cell.
 72. The method of claim 71, wherein receiving the electromagnetic beam includes receiving an externally-applied laser signal.
 73. The method of claim 69, wherein the remote-controlled vehicle is maneuvered to follow the electromagnetic beam using a plurality of electromagnetic sensors, each of the electromagnetic sensors generating a sensor output indicative of an intensity of electromagnetic energy received by the electromagnetic sensor from the electromagnetic beam.
 74. The method of claim 73, further comprising maneuvering the remote-controlled vehicle to generally equalize the sensor output of each of the electromagnetic sensors such that the electromagnetic beam is received generally evenly by the electromagnetic sensors.
 75. The method of claim 73, further comprising maneuvering the remote-controlled vehicle relative to the source of the electromagnetic beam such that the remote-controlled vehicle maintains a predetermined distance from the source of the electromagnetic beam.
 76. The method of claim 73, further comprising receiving external commands to adjust a response of the remote-controlled vehicle to the electromagnetic beam.
 77. The method of claim 69, wherein the remote-controlled vehicle includes an airborne vehicle.
 78. The method of claim 77, wherein the airborne vehicle includes a hovering vehicle configured to generate sufficient lift to support the airborne vehicle aloft.
 79. The method of claim 77, further comprising optimizing a speed of the at least one rotor to optimize power consumption of the at least one rotor.
 80. The system of claim 77, wherein the airborne vehicle includes a lighter-than-air vehicle.
 81. The method of claim 69, wherein the remote-controlled vehicle includes a land-based vehicle.
 82. The method of claim 69, wherein the remote-controlled vehicle includes a land-based vehicle.
 83. The method of claim 69, wherein the remote-controlled vehicle includes a water-based vehicle configured to operate at least one of on the surface and under the surface of a body of water.
 84. The system of claim 69, wherein the remote-controlled vehicle includes a space-based vehicle configured to operate in at least a partial vacuum. 